CHICAGO (Reuters) - Two of the largest and longest studies
so far show a "brain pacemaker" can effectively treat
depression and obsessive-compulsive disorder (OCD), researchers
said on Friday.

Devices implanted in the chest, with leads that send
electrical impulses to parts of the brain, have already been
approved to treat movement disorders, such as Parkinson's
disease, essential tremor and dystonia.

Dr. Ali Rezai, head of neurosurgery at the Cleveland
Clinic, who led the studies, said the technique known as deep
brain stimulation helped the most severely depressed patients
improve significantly.

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Researchers from Butler Hospital/Brown Medical School,
Massachusetts General Hospital and Harvard Medical School were
also involved in the depression study.

Seventeen patients, diagnosed as having major depressive
disorder, were followed for a year and demonstrated overall
improvement in mood as well as social and occupational
functioning, he said.

"These were severely depressed patients, the most
depressed," Rezai said in an interview.

Patients included in the study had been depressed for at
least five years, and were unresponsive to drug treatment or
electric shock therapy, he said.

The brain pacemaker, manufactured by Medtronic Inc, was
also effective in treating OCD, said Rezai, who was in Chicago
to present the findings to the American Association of
Neurological Surgeons meeting next week.

OCD is a psychiatric anxiety disorder marked by recurrent
and persistent thoughts and impulses, such as uncontrollable
and repeated hand washing.

St. Jude Medical Inc is currently conducting a similar
trial using a brain pacemaker to treat depression.

Rezai said the St. Jude trial affects a similar area of the
brain and is likely to generate similar findings.

He said there were no serious side effects in using the
Medtronic device.

The trial treating OCD included 26 patients who were
followed for three years and also showed marked improvement.

Butler Hospital/Brown University, University of Florida and
University of Leuven also contributed to the OCD study.

Medtronic has an application before the U.S. Food and Drug
Administration for approval to use deep brain stimulation for
OCD.

A clinical trial using the treatment for severe depression
will be initiated this year.

The FDA in 2005 approved Cyberonics Inc implantable device
for treatment-resistant depression. It sends signals to the
brain via the vagus nerve in the neck.